FRESNO, Calif. -- The lush backyard of a small California eldercare home has turned out to be the source of the poisonous wild mushrooms a caretaker made into a soup and fed to residents, killing two women.

The caretaker had no idea the mushrooms that had sprouted after recent rains were toxic, law enforcement officials said Tuesday. She was among the four others who were hospitalized Friday after six people ate the toxic soup Thursday night.

"The caretaker just didn't know, and she went outside and picked these mushrooms and made dinner, and she ate some of it herself," said Lt. Mark Reed of the Placer County sheriff's office. "It's definitely a sad, sad thing."

Sheriff's investigators were quickly able to pinpoint the soup as the source of the poisonings, Reed said, because the only person living at the home who did not eat dinner that night did not fall ill.

"She didn't eat it. They said she was an ornery lady and didn't want to eat," Reed said.

Food regulations for the California Department of Social Services do not prohibit the use of foraged ingredients in food, though they do prevent the use of home-canned foods and things such as unpasteurized milk, and meat that isn't inspected by state or federal authorities.

Spokesman Michael Weston did not respond to emails asking whether the department is considering modifying its food service requirements in light of the poisonings.

Weston said the state has begun an investigation into the incident at the Gold Age Villa, a six-bed care facility in Loomis run since 2007 by Raisa Oselsky. A one-page complaint released Tuesday said "staff fed clients poisonous mushrooms" and "further investigation" is needed.

"The department is investigating the case to determine if any licensing regulations were violated," he said.

Repeated calls to Oselsky's cellphone were not returned, nor were messages left on the answering machine at Gold Age Villa, where potted plants line the backyard and colorful vines climbs trellises.

Meanwhile, the family that owns the senior care facility issued a statement expressing profound grief over the incident.

"We are asking God to comfort all of our residents and their loved ones through the difficulty of this unintentional tragic event," said Michael Borisov, the son-in-law of the care home's owners, in a prepared statement to News10 in Sacramento.

"Some of you have been a part of our family for years, and all of you are very dear to us. We are grieving with you and our prayers are for you," he said.

Investigators said the woman who prepared the soup is an immigrant, but they were unsure how recently she had come to the U.S.

"She just thought it was OK to use them," Reed said. "I don't know how long she has been in the country."

In Northern California, it is the season for wild chanterelle mushrooms, a highly sought variety -- and also the amanita species of mushrooms, which includes the descriptively named "death cap" and "death angel" varieties. Young poisonous North American amanitas often look like an edible version of a wild mushroom popular in Asia.

The California Department of Public Health periodically issues warnings about consumption of wild mushrooms, especially after someone eats a poisonous variety and falls ill. The state recorded 1,700 cases of mushroom-related illnesses from 2009 to 2010, including two deaths.

Placer County sheriff's officials have called the deaths of Barbara Lopes, 86, and Teresa Olesniewicz, 73, an accident. Family members told the News10 that Olesniewicz was aware that she had been poisoned before she died.

The names of the other victims have not been released.

"It's quite a horrifying story," said Dena Erwin, a spokeswoman for the sheriff's office.